Polyaxial bone screw

ABSTRACT

A fastening system for bone screws used in spinal fixation systems for reshaping the spine of a patient. The bone screw has threads on one end for anchoring in the spine. The other end has a spherical head with a multi sided recess formed therein for engagement with an appropriate driving tool. The system includes a stabilizing rod, a saddle member, a cap member and a set screw with at least one bone screw having a outer diameter that exceeds the diameter of a cavity formed in the saddle, wherein placement of the bone screw is made possible by matching the threads of the set screw to the threads of the bone screw. The head of the bone screw providing proper positioning of the stabilization rod within the patient.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-In-Part of U.S. patent applicationSer. No. 11/749,615, filed May 16, 2007, entitled, “Polyaxial BoneScrew”, the entire disclosure of which is incorporated herein byreference.

FIELD OF THE INVENTION

This invention is directed to spinal implant systems and, in particular,to a multi-component adjustable implant system and polyaxial bone screwand connector kit.

BACKGROUND OF THE INVENTION

For individuals with spinal pathologies, the development of spinalfixation devices represents a major medical breakthrough. Surgicallyimplanted fixation systems are commonly used to correct a variety ofback structure problems, including those which occur as a result oftrauma or improper development during growth. These fixation systemstypically include one or more stabilizing rods aligned in a desiredorientation with respect to a patient's spine. Additionally, anchoringscrews are inserted into the patient's spinal bones, and a series ofconnectors are used to rigidly link the rods and anchors.

A variety of designs exist, with each design addressing various aspectsof the difficulties that arise when one re-shapes an individual's spineto follow a preferred curvature. Unfortunately, known spinal implantsystems often correct one set of problems only to create new ones.

Common to spinal implant systems is the necessity for proper anchoringto the bone so as to provide support for the aforementioned components.While bone screws are commonly used for anchoring, they are limited intheir positioning due to the design of component pieces. Numerouspatents are directed to component design in order to accommodate thebone screw, yet few patents are directed to making the assembly ascompact as possible to lessen the stress on the individual who must livewith the object within their body.

For this and other reasons, screws located in bone structure typicallyuse a specially designed clamp to attach to a component such as analignment rod. A problem with specially designed clamps is that bonestructure cannot be determined until the patient's bone is exposedcausing the necessity of a large inventory of various sized clamps to beon hand during surgery because the screws and clamps are typicallypre-assembled with respect to size, e.g. a larger screw requires alarger clamp, during assembly of the screw and the saddle. Typically ascrew is passed through an aperture at the bottom portion of a saddle,therefore the aperture must be large enough for passage of the threads,the spherical portion of the screw must be larger than the threads andthe aperture so that the spherical portion will contact the seat whichextends around the aperture. A further limitation of the prior artrelates to the requirement of a larger saddle for larger screwdiameters. The larger saddle complicates the placement of the screw toprevent impingement to adjacent body structures.

In the current art, even if a clamp combination is predicted, insertionof the screw may still require angular insertion due to muscle or tendernerve locations. The result is a bone screw which exerts unpredictableforces upon attachment to component connectors. Further, any movement ofmuscle and other tissue increases the difficulty of the operation andcan be a major trauma to a person.

A conventional bone screw consists of a single shaft with a coarsethread at one end for threading into the bone and a machine thread atthe other end for coupling to components. Another type of bone screw hasa U-shaped top which acts as a saddle for attachment to an alignmentrod. If the screw is placed incorrectly for any reason, the rod clampmust be made to accommodate the position.

A number of patents exist which demonstrate the reliance on the saddletype screw support and various designs to accommodate the problem.

U.S. Pat. No. 5,133,717 sets forth a sacral screw with a saddle support.Disclosed is the use of an auxiliary angled screw to provide thenecessary support in placing the screw in an angular position forimproved anchoring.

U.S. Pat. No. 5,129,900 sets forth an attachment screw and connectormember that is adjustably fastened to an alignment rod. An oblong areaprovided within each connector member allows minute displacement of thealignment rod.

U.S. Pat. No. 4,887,595 discloses a screw that has a first externallythreaded portion for engagement with the bone and a second externallythreaded portion for engagement with a locking nut. The disclosureillustrates the use of a singular fixed shaft.

U.S. Pat. No. 4,946,458 discloses a screw which employs a sphericalportion which is adapted to receive a locking pin so as to allow oneportion of the screw to rotate around the spherical portion. A problemwith the screw is the need for the locking pin and the inability of thebase screw to accommodate a threaded extension bolt.

U.S. Pat. No. 5,002,542 discloses a screw clamp wherein two horizontallydisposed sections are adapted to receive the head of a pedicle screw foruse in combination with a hook which holds a support rod at anadjustable distance.

U.S. Pat. No. 4,854,304 discloses the use of a screw with a top portionthat is adaptable for use with a specially designed alignment rod topermit compression as well as distraction.

U.S. Pat. No. 4,887,596 discloses a pedicle screw for use in coupling analignment rod to the spine wherein the screw includes a clamp permittingadjustment of the angle between the alignment rod and the screw.

U.S. Pat. No. 4,836,196 discloses a screw with an upper portion designfor threadingly engaging a semi-spherical cup for use with a speciallydesigned alignment rod. The alignment rod having spaced apart coverturesfor receipt of a spherical disc allowing a support rod to be placed atangular positions.

U.S. Pat. No. 5,800,435 sets forth a modular spinal plate assembly foruse with polyaxial pedicle screw implant devices. The device includescompressible components that cooperatively lock the device alongincluded rails.

U.S. Pat. No. 5,591,166 discloses an orthopedic bone bolt and bone plateconstruction including a bone plate member and a collection offasteners. At least one of the fasteners allows for multi-angle mountingconfigurations. The fasteners also include threaded portions configuredto engage a patient's bone tissue.

U.S. Pat. No. 5,569,247 discloses a multi-angle fastener usable forconnecting patient bone to other surgical implant components. The '247device includes fastening bolts having spherical, multi-piece heads thatallow for adjustment during installation of the device.

U.S. Pat. No. 5,716,357 discloses a spinal treatment and long bonefixation apparatus. The apparatus includes link members adapted toengage patient vertebrae. The link members may be attached in achain-like fashion to connect bones in a non-linear arrangement. Theapparatus also includes at least one multi-directional attachment memberfor joining the link members. This allows the apparatus to be used informing a spinal implant fixation system.

Another type of spinal fixation system includes rigid screws that engagethe posterior region of a patient's spine. The screws are adapted withrod-engaging free ends to engage a support rod that has been formed intoa desired spine-curvature-correcting orientation. Clamping members areoften used to lock the rod in place with respect to the screws. Insteadof clamping members, other fixation systems, such as that disclosed inU.S. Pat. No. 5,129,900, employ connectors that join the support rodsand anchoring screws. The connectors eliminate unwanted relative motionbetween the rod and the screws, thereby maintaining the patient's spinein a corrected orientation.

Unfortunately, although these so-called rigid screw fixation systems canalter the curvature of a patient's spine, they can also be difficult toinstall. In this type of system, the anchoring screws must be secured ina region that is strong/rigid enough to support thecharacteristically-large loads typically transferred from the supportrods. As a result, the number of suitable anchoring locations islimited. Typically, these screws are anchored into the posterior regionof a patient's spinal column or into pedicle bone. With rigid screwsystems, installation requires bending a support rod into a path thatwill not only correct the shape a patient's spine but that will alsoengage each of the installed anchoring screws. Achieving a proper fitbetween all of the components while contending with the constraintsencountered during surgery is often difficult. In severe cases, asuitable fit may not be achieved and the surgery will be unsuccessful.

Additionally, the nature of the installation process required for rigidscrew fixation systems often subjects the system components topre-loading that unduly stresses the interface between the patient'sbone and the employed anchoring screws. With these designs, as a patientmoves about during daily life, the system components may becomeseparated from the supporting bone. Corrective surgery to reattachanchoring screws exposes an already-weakened region to additional traumaand presents the risk of additional damage.

Other spinal fixation systems employ adjustable components. For example,U.S. Pat. No. 5,549,608 includes anchoring screws that have pivotingfree ends which attach to discrete rod-engaging couplers. As a result,the relative position of the anchoring screws and rods may be adjustedto achieve a proper fit, even after the screw has been anchored into apatient's spinal bone. This type of fixation system succeeds in easingthe rod-and-screw-linking process. This adjustment capability allows thescrews to accommodate several rod paths. Unfortunately, some adjustablefixation systems tolerate only limited amounts of relative adjustmentbetween components, operating best when loaded in one of severalpreferred arrangements. As a result, many prior art adjustable fixationsystems are suitable for only a few situations.

Additionally, many adjustable fixation systems are prone to post-surgerycomponent loosening. As a patient moves about during day-to-day living,their spine is subjected to a seemingly-endless amount of dynamicloading. Almost all activity requires some form of back motion; overtime, this cyclic movement tends to work the components of manyadjustable fixation systems loose.

Some adjustable spinal fixation systems include locking mechanismsdesigned for long-term, post-surgery securement of the systemcomponents. Although capable of being locked in place, these systems areoften difficult to secure, requiring an excess of tools during theinstallation process. The need for extra tools, such as those requiredto shave, to apply anti-torque, or crimp key portions of a fixationsystem, increasing surgical risk by adding complexity and increasing thenumber of required steps. Although locking-component fixation systemsexist, many of them unduly increase the dangers of back implant surgeryto an unacceptable level.

Hardware-intensive fasteners are disclosed in U.S. Pat. No. 5,549,608,in which anchoring screws are fitted with wrenching flats that allow ananchoring screw to be attached to a patient's spinal bone with the flatsbeing trimmed away once the screw is in place. Clamping nuts are thenused to secure the anchoring screws to included stabilizing rods.

Additionally, many spinal fixation systems do not permit componentrepairs. If, for example, a threaded portion of a connecting memberbecomes stripped or cross-threaded, the entire connector must be slidoff of the associated stabilizing rod. Often, such removal produces anundesirable domino-effect, requiring that several connectors be slid offto allow removal of the damaged connector. Such requirements addunnecessary difficulty to an already-complex procedure.

The bone screws shown and described in U.S. Pat. No. 5,628,740 and U.S.Pat. No. 6,050,997 have a bone screw with a spherical cavity in theproximal end. A toggle bolt with a spherical distal end is inserted intothe cavity in the bone screw. A collet is forced into the sphericalcavity superior to the spherical end of the toggle bolt. A supportcollar or attachment cap is placed over the toggle bolt and tighteneddown. This forces the retention collet to engage the spherical portionof the toggle bolt and the inside of the spherical cavity locking thetoggle bolt in a selected angular disposition. This system requiresextremely accurate machining of the threaded components to result in anoptimum frictional fit. Further, because the collet is a ring, with afixed inner diameter, there is only one correct size for the sphericalcomponents. Finally, any deformation of the ring will lessen theover-all frictional contact by creating wrinkles or ridges on thecollet.

U.S. Pat. No. 4,419,026 to Leto discloses a split ring camming internallocking device used with telescoping tubular members for transportingliquids. The ring is split for flexing to fit around the internal tubeand for resiliently sealing against the external tube.

The bone screw described in U.S. Pat. Nos. 7,128,743 and 6,537,276 and6,261,287 and 6,090,110 includes an annular head with an opening and aslot. Each slot extends into the opening and is provided with internallythreaded portions. A securing screw is screwed into the slot. Arelatively stiff threaded rod is inserted into the opening the pediclescrew and is secured in place by the securing screws. In an alternateembodiment the screw includes a shaft with an upper end formed as aball. A cage cooperates with the ball and further includes a passage toreceive a threaded rod. The cage also includes a threaded portion forreceiving a securing screw for securing the rod to the cage and screw.

The bone screw described in U.S. Pat. No. 6,726,689 includes a lockingor securing element wherein the threads on the implant member andsecuring element are configured to prevent splaying of the arms of theimplant member.

Thus, what is needed is a spinal fixation system that includes theadvantages of known devices, while addressing the shortcomings theyexhibit. The system should allow component adjustment duringinstallation, thereby enabling satisfactory correction of a wide varietyof spinal deformities. The system should also include a componentlocking mechanism that is simple and reliable. The system should alsoinclude mounting hardware that secures with a minimum of tools and thatallows modular replacement of components damaged during installation.The system should also include tools and components for the lockingmechanism developing a compression fit between components withoutadditional torque on the bone-screw interface.

SUMMARY OF THE INVENTION

The present invention is a fastening system for bone screws used inspinal fixation systems for reshaping the spine of a patient. The bonescrew has threads on one end for anchoring in the spine. The other endhas a spherical head with a multi sided recess formed therein forengagement with an appropriate driving tool. The stabilizing rods areshaped and aligned to impart a preferred curvature to a patient's spine.

Attaching each anchoring assembly to a stabilizing rod forces apatient's back into a surgeon-chosen shape. Stabilizing rods may be usedsingly, or in pairs, depending upon the type of correction required. Therods vary in size, but typically extend between at least two vertebrae.

During the surgical procedure it is common to employ screws of varyingdiameter threads dependent on the shape and quality of the boneformations presented by the patient. Likewise it is important that theoverall size and shape of the connecting elements be kept to an absoluteminimum without jeopardizing the structural integrity of the components.In addition, it is also very desirable from a cost and safetyperspective to minimize the number of component parts that aremaintained in inventory and subsequently brought into the operating roomto be used during the procedure.

Accordingly, it is an objective of the present invention is to provide afastener system for polyaxial bone screws of varying size capable ofcooperation with a common base member whose profile is minimized whileat the same time optimizing the structural integrity of the base member.

It is another objective of the present invention to provide a polyaxialbone screw assembly for a spinal fixation system that permits componentadjustment during installation, thereby enabling satisfactory correctionof a wide variety of spinal deformities.

It is still another objective of the present invention to provide asimple, easy to use, reliable and cost effective implant system.

It is an additional objective of the present invention to provide a bonescrew assembly that includes a fastener member that is simple andreliable.

It is yet another objective of the present invention to provide a spinalfixation system that includes mounting hardware which requires a minimumnumber of tools.

It is also an objective of the present invention to provide a spinalfixation system that allows modular replacement of damaged components.

Still another objective is to teach the use of a rod clamping devicehaving a polyaxial bone screw wherein the rod claim saddle permitspassage of a bone screw having a diameter larger than the cavityprovided in a saddle.

Other objectives and advantages of this invention will become apparentfrom the following description taken in conjunction with theaccompanying drawings wherein are set forth, by way of illustration andexample, certain embodiments of this invention. The drawings constitutea part of this specification and include exemplary embodiments of thepresent invention and illustrate various objects and features thereof.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a pictorial view of the spinal fixation system of the presentinvention;

FIG. 2 is a pictorial view of the anchoring device and associatedcomponents of the instant invention utilizing one of the larger screwelements;

FIG. 3 is a pictorial view of the anchoring device and associatedcomponents of the instant invention utilizing a screw of a smallerdimension than that shown in FIG. 2;

FIG. 4 is a cross sectional view of the larger polyaxial bone-engagingscrew and associated components in an assembled condition;

FIG. 5 is a section view of a polyaxial bone-engaging screw with thehead member as shown in FIG. 4 during an intermediary stage of assembly;

FIG. 6 is a cross sectional view of a smaller polyaxial bone-engagingscrew and associated components in an assembled condition;

FIG. 7 is a section view of a polyaxial bone-engaging screw as with thehead member as shown in FIG. 6 during an intermediary stage of assembly;

FIG. 8 is a cross sectional view of the polyaxial screw and head memberduring an intermediary stage of assembly;

FIG. 9 is an enlarged sectional view of the head member and thepolyaxial screw and the relationship between the threads of thepolyaxial screw and the threads on the interior wall of the head member,as shown in FIG. 8;

FIG. 10 is a perspective view of the head member of the presentinvention;

FIG. 11 is a cross sectional view of the head member of the presentinvention;

FIG. 12 is a pictorial view illustrating the set screw of the presentinvention;

FIG. 13 is a perspective view of the cap member of the presentinvention;

FIG. 14 is a side view of the cap member of the present invention;

FIG. 15 is a sectional view of the cap member seated within the headmember (the screw being omitted for purposes of clarity only as willdescribed in the detailed description to follow);

FIG. 16 is an isometric view of the head of the instant invention;

FIG. 17 is an isometric view of the cap member of the present invention;

FIG. 18 is a pictorial view of the screw assembly illustrating the sixtydegrees of polyaxial motion of the screw with respect to the headmember; and

FIGS. 19 through 22 are perspective views of four different sized screws(by way of example only) that can be used with the polyaxial screwsystem.

FIG. 23 is a perspective view of an additional embodiment of the spinalfixation system.

FIG. 24 is a side elevation view of the spinal fixation system of FIG.23.

FIG. 25 is a cross sectional elevation view of the spinal fixationsystem of FIG. 24.

FIG. 26 is a cross sectional elevation view of the spinal fixationsystem of FIG. 23.

FIG. 27 is an enlarged perspective view of an additional form of rodbase member.

FIG. 28 is an enlarged perspective view of an additional form of setscrew.

FIG. 29 is a cross sectional elevation view of the addition form of rodbase member of FIG. 27.

Like numbers used throughout this application represent like or similarparts and/or construction.

DETAILED DESCRIPTION OF THE INVENTION

It is to be understood that while a certain form of the invention isillustrated, it is not to be limited to the specific form or arrangementof parts herein described and shown. It will be apparent to thoseskilled in the art that various changes may be made without departingfrom the scope of the invention and the invention is not to beconsidered limited to what is shown in the drawings and described in thespecification.

Now with reference to FIG. 1, the spinal fixation system 1 includes aplurality of polyaxial screws 4 each in cooperative relationship to arod base member 2 for fixedly securing a stabilizing rod 3.

FIGS. 2 and 3, illustrate two anchoring devices wherein the diameter ofthe threaded shank portion 6 a of the polyaxial screw 4(a) in FIG. 2(D1) is larger than the threaded shank portion 6(b) the polyaxial screw4(b) illustrated in FIG. 3 (D2).

FIGS. 4, 5, 6 and 7 illustrate polyaxial screws 4(a) and 4(b) eachhaving a spherical head 5. The spherical head 5 includes a tool socket18 at the top portion thereof to receive a tool (not shown) constructedand arranged to transfer rotary and/or linear force to thread the screwinto the patient's bones. Rod base member 2, which is also shown in moredetail in FIGS. 10, 11, 15, and 16, is generally cylindrical in shapeand includes a pass-through aperture that extends between the upperportion 32 and an aperture in the lower portion 34. The rod base member2 also includes two diametrically opposed U-shaped slots 15(a) and15(b), as shown in detail in FIG. 10, in the side wall 19 which are openat the upper end 32 of the rod base member 2 and extend downwardstowards the lower portion 34 of the rod base member. The side wall 19includes a pair of arms 24A, B that have edges defining portions of theslots 15(a), (b) and the slots forming a rod receiving channel. The rodbase member 2 also includes a helical seating surface 7 at the lowerportion 34 of the rod base member. The spherical head 5 of the polyaxialscrew, 4 a or 4 b, is designed to operatively cooperate with the helicalseating surface 7 on the rod base member 2 for polyaxial movement of thescrew with respect to the rod base member 2. The helical seating surface7 provides multiple points of contact not necessarily in the same planethereby reducing the chances of slippage between the spherical head 5and helical bearing surface 7 after the parts are securely assembled andthe set screw is tightened. It should also be noted that seats having ashape other than helical could be used without departing from the scopeof the invention which may include, but should not be limited to, frustoconical, spherical, sharp edges, radiused edges, segmented and suitablecombinations thereof. The polyaxial screw 4 is properly positionedwithin rod base member 2 against the seat 7. A cap member 8, which isalso shown in more detail in FIGS. 13, 14 and 17, can then fit into thelower portion of the pass-through aperture 33. The cap member 8 isgenerally cylindrical in shape and is provided with a generally flat 30,cylindrical (not shown) or other suitable surface on one end andgenerally hollow semi spherical surface 17 on the opposite end sized forcooperation with the head 5 of the screw 4. The cap member 8 furtherincludes an aperture 9 which extends between the end surface 30 of thecap member and the semi spherical surface 17 on the opposite end of thecap member. Aperture 9 permits insertion of a driving tool (not shown)into socket 18 on the head 5 of the polyaxial screw for threading thescrew 4 into the patient's bone.

Referring to FIGS. 13, 14 and 17, the cap member 8 further includesresilient friction fingers 20 on opposite sides of the cylindrical wallsas well as annular ridges 21 and 22 around the circumference of thecylindrical cap member located near the top and bottom thereof. The rodbase member 2 includes an annular interference diameter 23 thatcooperates with annular ridge 21 of the cap member 8 once the cap memberis pressed past the interference diameter 23 to prevent the cap fromfalling out of position once installed. In addition, friction fingers 20serve to maintain the semi spherical seat 17 and the spherical head 5 inoperative engagement wherein the screw has polyaxial freedom of motionand yet will hold a particular set orientation between the screw and thehead until a sufficient amount of force is applied thereto. Thisparticular feature assists the surgeon in positioning the rod basemember relative to an inserted bone screw prior to final securement ofthe rod member 3.

A set screw 10, shown in more detail in FIG. 12, is generallycylindrical in shape with external threads 11 on the cylindrical surfaceand opposed generally flat ends. One of the flat ends of the set screw10 includes a tool socket 13 to provide operative engagement with anappropriate driving tool. The internal cavity of the rod base member 2is provided with threads 12 having a form, pitch and size to conform tothe threads 11 of the set screw. In a most preferred embodiment thethreads are buttress style threads that may include a back tapered uppersurface to provide anti-splaying characteristics to the rod base member2. However, it should be noted that other thread types suitable forsecuring the instant assembly together may be utilized without departingfrom the scope of the invention. The set screw 10 will be torqued intothe rod base member 2 with a force of approximately 100 inch pounds toensure that the connector and rod member are firmly locked in place. Theinternal cavity of the rod base member 2 also includes threads 14 whichextend from the lower end of threads 12 through to the lower end of therod base member 2. The purpose of these threads will be discussed inmore detail with respect to FIGS. 5, 7 and 9.

Referring to FIGS. 2 and 3, polyaxial screws 4 a and 4 b are illustratedeach having threads of varying diameter in an assembled condition with astabilizer rod 3, a rod base member 2, a cap member 8 and a set screw10.

Referring to FIGS. 5 and 7, the unique relationship between the rod basemember 2 and the polyaxial screws 4(a) and 4(b) and their respectivethreads 6(a) and 6(b) is illustrated. Turning to FIG. 5, it can be seenthat as the larger diameter screw thread is inserted into the interiorcavity of rod base member 2, the threads 6(a) on screw 4(a) includesubstantially the pitch to engage the screw threads 12 on the upperportion of the interior cavity and subsequently engage threads 14 whichextend from the lower end of threads 12 through to the lower end of rodbase member 2. In this manner, the polyaxial screw can be screwed intoposition wherein the spherical head 5 rests on the helical seatingsurface 7. It should be noted that this construction permits a bonescrew having a larger diameter than the pass through aperture 33 of therod base member 2 to be inserted therethrough, whereby the sphericalhead portion of the bone screw will still engage the seat portion 7 ofthe rod base member 2. It should also be noted that the thread form andpitch of the bone screw do not have to match the exact thread form andpitch of the rod base member for operation, the pitch and form of thethread on the bone screw need only be constructed and arranged tothreadably pass through the pass through aperture 33 without significantinterference between the two components. FIG. 7 illustrates therelationship between the rod base member 2 and a polyaxial screw 4(b)with a smaller diameter screw thread 6(b). As can be seen in FIG. 7,there is sufficient clearance between the outer diameter of the threads6(b) and walls of the pass-through aperture to easily allow the screw tobe inserted through the pass-through aperture 33 until the head 5 restson the helical seat 7 of the rod base member 2. It should be noted thatthis feature also permits the interchangeability of screws of varyingdiameter while utilizing the same rod base member (s), cap member (s),and set screw (s). This construction also permits the instant inventionto be provided in a kit form wherein a rod base member, cap member andset screw may be provided with a plurality of bone screws havingdifferent outer diameters allowing a surgeon to choose a bone screw forthe specific patient condition. This feature also allows a surgeon toincrease the diameter of screw in cases where the smaller diameter screwfails to achieve the proper purchase to the bone during tightening ofthe bone screw or where the patient's bones are more fragile ordeteriorated than expected.

FIGS. 10, 11, 15 and 16 illustrate the rod base member 2 and theU-shaped slots 15(a) and 15(b) as well as threads 12 and 14 within theinternal cavity. Recesses 16(a) and 16(b) on the external walls of thehead 2 are designed to cooperate with assembly tools to provide forcesto counteract the tightening of the set screw. In this manner, loadsexerted on the set screw are substantially prevented from beingtransferred to the bone screw bone interface.

FIG. 18 illustrates the range of infinite angular adjustment between therod base member 2 and the polyaxial screw 4 prior to tightening of setscrew 10. It is contemplated, in a non-limiting embodiment, that thescrew be capable of about 60 degrees of polyaxial motion within a 360degree range of movement.

FIGS. 19 through 22 illustrate polyaxial screws 4 each having threadedsections of different external diameter showing, by way of example only,four separate screws; 8.5 mm (FIG. 19), 7.5 mm (FIG. 20), 6.5 mm (FIG.21) and 5.5 mm (FIG. 22). It should be noted, that the spherical headportion 5 of the bone screw(s) 4 is substantially the same size acrossthe full range of bone screw diameters.

The spinal fixation system 1 (FIG. 1) is assembled in the followingmanner. A polyaxial screw 4 is either slid through or threaded throughthe pass-through aperture of a rod base member 2 until the sphericalhead 5 of the polyaxial screw 4 rests on the helical seating surface 7at the lower end portion of the rod base member. Thereafter the capmember 8 is positioned in the pass-through aperture 33 of the rod basemember in such a manner so that the generally hemispherical surface 17of the cap member mates with the upper portion of the spherical head 5of the bone screw. This step also engages the annular ridges 21, 22 withthe interference diameter 23 in the pass-through aperture. A tool isthen inserted through aperture 9 and into tool socket 18 on the top ofspherical head 5 for threading the screw into the patient's bone. One ormore additional screw(s) are inserted into the patient's bones in asimilar fashion. A stabilizing rod 3 is positioned within the U-shapedslots 15(a) and 15(b) of each rod base member 2. The rod 3 bears againstthe flat surface of the cap member 8. A set screw 10 is threaded intothe upper end of each rod base member 2. Once the angular orientation ofthe stabilizing rod with respect to the polyaxial screws is properlyestablished the set screws are securely tightened so as to fix thestabilization rod in a proper position.

Referring to FIGS. 1 through 22, the spinal fixation system 1 ispreferably formed from rigid, biocompatible materials. One suchpreferred material is titanium; however, other materials well known inthe art may also be used. It should also be noted that any or all of thecomponents could be made from bio-resorbable materials or could becoated with bone growth materials that are well known in the art withoutdeparting from the scope of the invention.

FIGS. 23-29 illustrate additional embodiments of the invention to thoseshown in FIGS. 1-22 and are similar in construction and use. Theillustrated set screw 10 and rod base member 2 are similar but havedifferences as described below, particularly with reference to the upperend of the rod base members 2 and the set screws 10. Now with referenceto FIG. 23, the spinal fixation system 1 includes a polyaxial screw 4 incooperative relationship to a rod base member 2 for fixedly securing astabilizing rod 3.

FIGS. 23 and 26, illustrate a fixation system 1 wherein the screw 4 hasa diameter of the threaded shank portion 6 a as described above butcould also have a threaded shank portion 6(b) also as described abovecooperating with the base member 2.

The illustrated polyaxial screw 4 has a spherical head 5. The sphericalhead 5 includes a tool socket 18 at the top portion thereof to receive atool (not shown) constructed and arranged to transfer rotary and/orlinear force to thread the screw 4 into a patient's bone. Rod basemember 2, FIGS. 27, 29, is generally cylindrical in shape and includes apass-through aperture 33 that extends between the upper portion 32 andan opening in the lower portion 34. The rod base member 2 also includestwo diametrically opposed U-shaped slots 15(a) and 15(b) in the sidewall 19 which are open at the upper end of the rod base member 2 andextend downwards towards the lower portion 34 of the rod base member.The side wall 19 includes a pair of arms 24A, B that have edges definingportions of the slots 15(a), (b) and the slots forming a rod receivingchannel. The rod base member 2 also includes a seating surface 7 at thelower portion 34 of the rod base member as described above. Thespherical head 5 of the screw 4, is designed to operatively cooperatewith the seating surface 7 on the rod base member 2 for polyaxialmovement of the screw 4 with respect to the rod base member 2. It shouldalso be noted that seat 7 can have any suitable shape such as helical,frusto conical, spherical, sharp edges, radiused edges, segmented andsuitable combinations thereof. The screw head 5 is properly positionedwithin rod base member 2 against the seat 7. A cap member 8, FIG. 26,can then fit into the lower portion of the pass-through aperture 33. Thecap member 8 is generally cylindrical in shape and is provided with agenerally flat, circular surface 30, or other suitable surface on oneend and generally hollow seating surface 17 on the opposite end sizedand shaped for cooperation with the head 5 of the screw 4. The capmember 8 further includes an aperture 9 which extends between the endsurface 30 and the semi spherical surface 17 on the opposite end of thecap member. Aperture 9 permits insertion of a driving tool (not shown)into socket 18 on the head 5 for threading the screw 4 into thepatient's bone.

The cap member 8 is as described above and can include resilientfriction fingers 20 on opposite sides of the cylindrical walls as wellas annular ridges 21 and 22 around the circumference of the cylindricalcap member located near the top and bottom thereof. The rod base member2 includes an annular interference diameter 23 that cooperates withannular ridge 21 of the cap member 8 once the cap member is pressed pastthe interference diameter 23 to prevent the cap from falling out ofposition once installed. In addition, friction fingers 20 serve tomaintain the seat 17 and the head 5 in operative engagement wherein thescrew 4 has polyaxial freedom of motion and yet will hold a particularset orientation between the screw and the head until a sufficient amountof force is applied thereto.

A set screw 10, shown in FIGS. 23, 26, 28, is generally cylindrical inshape with external threads 11A on the cylindrical surface and opposedends that are shown as generally flat. One of the flat ends of the setscrew 10 includes a tool socket 13 to provide operative engagement withan appropriate driving tool. The internal cavity of the rod base member2 is provided with threads 12A adjacent to and extending into the cavityfrom the end 32. The threads 12A have a form, pitch and size to conformto the threads 11A of the set screw 10. In a preferred embodiment thethreads 11A, 12A are different from the threads 6 a and can be anysuitable machine thread having a pitch less than the pitch of thethreads 6 a. The threads 11A, 12A have a pitch preferably finer thanabout 13 thread per inch and preferably finer than about 16 threads perinch. Any suitable thread shape may be provided such as Acme, square orany other suitable machine thread shape. A thread shape to provideanti-splaying characteristics as described above to the rod base member2 may also be used. The threads 12A in the rod base member 2 extendinwardly from the end 32 about ⅓ the length of the aperture 33. Theinternal cavity of the rod base member 2 also includes the threads 14Awhich extend from the lower end of threads 12A toward the lower end 34of the rod base member 2. In a preferred embodiment, the remainder ofthe length or a substantial portion of the remainder of the aperture 33may have threads 14A compatible with the threads 6A and are differentfrom the threads 11A, 12A. The threads 14A have a pitch preferablycoarser than about 10 threads per inch and more preferably coarser thanabout 8 threads per inch. The threads 6A may interfere with the threads14A, 12A when the screw 4 is installed in the rod base member 2 asdescribed above. As shown, the threaded shank with the threads 6A has adecreasing thread diameter toward the distal end 40 of the shank. Thethreads 11A, 12A have a substantially uniform thread diameter along thelength of the respective threaded sections. The set screw 10 will betorqued into the rod base member 2 with a force of approximately 100inch pounds to ensure that the connector and rod member are firmlylocked in place.

The screw 4 has threads 6 of varying diameter in an assembled conditionwith a stabilizer rod 3, a rod base member 2, a cap member 8 and a setscrew 10.

Referring to FIGS. 5 and 7, the unique relationship between the rod basemember 2 and the polyaxial screws 4(a) and 4(b) and their respectivethreads 6(a) and 6 (b) is illustrated. That description is applicable tothe screw 4 and threads 6A and 6B and their variants as described above.

FIGS. 27, 29 illustrate the rod base member 2, the U-shaped slots 15(a)and 15(b) as well as threads 12A and 14A within the internal cavity.Recesses 16(a) and 16(b) on the external walls of the base member 2 aredesigned to cooperate with assembly tools to provide forces tocounteract the tightening of the set screw. In this manner, loadsexerted on the set screw are substantially prevented from beingtransferred to the bone screw bone interface.

All patents and publications mentioned in this specification areindicative of the levels of those skilled in the art to which theinvention pertains. All patents and publications are herein incorporatedby reference to the same extent as if each individual publication wasspecifically and individually indicated to be incorporated by reference.

It is to be understood that while a certain form of the invention isillustrated, it is not to be limited to the specific form or arrangementherein described and shown. It will be apparent to those skilled in theart that various changes may be made without departing from the scope ofthe invention and the invention is not to be considered limited to whatis shown and described in the specification and any drawings/figuresincluded herein.

One skilled in the art will readily appreciate that the presentinvention is well adapted to carry out the objectives and obtain theends and advantages mentioned, as well as those inherent therein. Theembodiments, methods, procedures and techniques described herein arepresently representative of the preferred embodiments, are intended tobe exemplary and are not intended as limitations on the scope. Changestherein and other uses will occur to those skilled in the art which areencompassed within the spirit of the invention and are defined by thescope of the appended claims. Although the invention has been describedin connection with specific preferred embodiments, it should beunderstood that the invention as claimed should not be unduly limited tosuch specific embodiments. Indeed, various modifications of thedescribed modes for carrying out the invention which are obvious tothose skilled in the art are intended to be within the scope of thefollowing claims.

1. A spinal fixation system for orthopedic rod implantation, comprising:a bone screw having a threaded shank portion and a substantiallyspherical head portion; a rod base member having a pair of uprightspaced apart arms defining a U-shaped channel, said rod base memberhaving an upper pass through aperture and a lower pass through apertureand an internal cavity extending between said upper pass throughaperture and said lower pass through aperture, said internal cavityincluding a threaded surface that extends the length of said internalcavity from said upper pass through aperture to said lower pass throughaperture to allow said threaded shank portion to pass through saidinternal cavity while retaining said spherical head portion, saidthreaded surface including a first thread portion having a first threadconfiguration and a second thread portion having a second threadconfiguration, said first thread configuration being different than thesecond thread configuration; a monolithic cap member positioned along anend of said spherical head portion, said cap member providing aspherical seating surface for an upper surface of said spherical headand a support base for a stabilizing rod placed within said U-shapedchannel, wherein the cap member includes annular ridges on thecylindrical wall of the cap member at the top and bottom thereof; and aset screw threadably engageable along said threaded surface of saidinternal cavity for engaging said stabilizing rod against said capmember wherein said cap member secures said rod base member in a fixedposition by frictional engagement with said spherical head portion ofsaid bone screw.
 2. The spinal fixation system of claim 1 wherein saidthreaded surface is adapted to engage said set screw and sized to allowunobstructed insertion of said bone screw threaded shank.
 3. The spinalfixation system of claim 1 wherein said lower pass-thru apertureincludes a seat member receptive to a lower surface of said sphericalhead.
 4. The spinal fixation system of claim 1 wherein said U-shapedchannel is further defined as two diametrically opposed openings on thewalls thereof wherein the stabilizing rod is positioned within the twoshaped openings.
 5. The spinal fixation system of claim 1 wherein thethreads on said set screw are configured to prevent splaying of said rodbase member.
 6. The spinal fixation system of claim 1 wherein saidmonolithic cap member is generally cylindrical in shape and is providedwith a flat surface on one end and generally semi spherical surface onan opposite end.
 7. The spinal fixation system of claim 6 wherein thecap member further includes an aperture which extends between the flatsurface on one end of the monolithic cap member and the semi sphericalsurface on the opposite end of the cap member.
 8. The spinal fixationsystem of claim 1 wherein the monolithic cap member further includesresilient friction fingers on the cylindrical wall thereof which are inopposed relationship to one another.
 9. The spinal fixation system ofclaim 1 wherein the threads of the first threaded portion are finer thanthe threads on the second threaded portion.
 10. The spinal fixationsystem of claim 1 wherein the rod base member includes an interferencediameter within the interior cavity that cooperates with the top annularridge to prevent the monolithic cap member from backing up.
 11. Thespinal fixation system of claim 1 wherein the monolithic cap memberincludes an aperture within the spherical seat.
 12. The spinal fixationsystem of claim 1 wherein the spherical head of the polyaxial screwincludes a multi sided tool socket.
 13. The spinal fixation system ofclaim 1 wherein the set screw includes a top and a bottom wall, saidbottom wall being generally flat and in abutting relationship to saidstabilizing rod, said top surface being generally flat and including amulti sided tool socket in said top surface for driving said set screw.14. A spinal fixation kit for orthopedic rod implantation, comprising:at least two bone screws, each said bone screw having a threaded shankportion and a substantially spherical head portion; a rod base memberhaving a pair of upright spaced apart arms defining a U-shaped channel,said rod base member having an upper pass through aperture and a lowerpass through aperture and an internal cavity extending between saidupper pass through aperture and said lower pass through aperture, saidinternal cavity including a threaded surface that extends the length ofsaid internal cavity from said upper pass through aperture to said lowerpass through aperture to allow said threaded shank portion of at leastone said bone screw to pass through said internal cavity while retainingsaid spherical head portion; a monolithic cap member positioned along anend of said spherical head portion, said cap member providing aspherical seating surface for an upper surface of said spherical headand a support base for a stabilizing rod placed within said U-shapedchannel, wherein the cap member includes annular ridges on thecylindrical wall of the cap member at the top and bottom thereof; and aset screw threadably engageable along said interior threaded surface ofsaid internal cavity for engaging said stabilizing rod against said capmember wherein said cap member secures said rod base member in a fixedposition by frictional engagement with said spherical head portion ofsaid bone screw.
 15. The spinal fixation system of claim 14 wherein saidthreaded surface is adapted to engage said set screw and sized to allowunobstructed insertion of at least one said bone screw having a threadedshank.
 16. The spinal fixation system of claim 14 wherein the threads onsaid set screw are configured to prevent splaying of said rod basemember.
 17. The spinal fixation system of claim 14 wherein saidmonolithic cap member is generally cylindrical in shape and is providedwith a flat surface on one end and generally semi spherical surface onan opposite end.
 18. The spinal fixation system of claim 17 wherein themonolithic cap member further includes an aperture which extends betweenthe flat surface on one end of the cap member and the semi sphericalsurface on the opposite end of the cap member.
 19. The spinal fixationsystem of claim 14 wherein the monolithic cap member further includesresilient friction fingers on the cylindrical wall thereof which are inopposed relationship to one another.
 20. The spinal fixation system ofclaim 14 wherein the threads of the first threaded portion are finerthan the threads on the second threaded portion.
 21. The spinal fixationsystem of claim 14 wherein the rod base member includes an interferencediameter within the interior cavity that cooperates with the top annularridge to prevent the monolithic cap member from backing up.
 22. Thespinal fixation system of claim 14 wherein the monolithic cap memberincludes an aperture within the spherical seat.
 23. The spinal fixationsystem of claim 14 wherein the spherical head of the polyaxial screwincludes a multi sided tool socket.
 24. The spinal fixation system ofclaim 14 wherein the set screw includes a top and a bottom wall, saidbottom wall being generally flat and in abutting relationship to saidstabilizing rod, said top surface being generally flat and including amulti sided tool socket in said top surface for driving said set screw.